1. Field of the Invention
The present invention relates to a load driving device for supplying a driving current to a load and an electrical device (for example, an optical disc driving device) using such a load driving device.
2. Description of Related Art
In a car navigation system, a car audio system, or a portable navigation system including an optical disc driving device that performs recording and reproduction on an optical disc such as a DVD (Digital Versatile Disc), a CD (Compact Disc), an MD (Mini Disc), or the like, a beam spot is formed on the recording surface of the optical disc by using a pickup lens to thereby perform data recording and reproduction on the optical disc. As an actuator for making fine adjustment of an optical pickup position, a focus coil, a tracking coil, a tilt coil, or the like is used.
The actuator coil for a pickup lens described above, although being a light, small component, is driven by flow of a relatively large current, and thus generates large heat and is easy to burn out.
Therefore, conventionally employed as techniques of protecting an actuator coil from overcurrent-induced burnout are a technique of muting all coil outputs when a maximum output of the actuator coil (condition in which an amplifier output is off-scale) is detected continuously for a certain period of time (for example, 300 [ms]), a technique of monitoring a power current of a driver driving a plurality of actuator coils to thereby control a peak current, a technique of monitoring a control signal of a driver with a DSP (Digital Signal Processor) in a software-based manner to thereby control a peak current, and a technique of detecting a drive voltage to a coil to thereby control a peak current.
As one of conventional technologies related to the above, JP-UM-H05-55798 (hereinafter, referred to as Patent Document 1) discloses and proposes a speed-controllable coil burnout preventing device for a blushless motor, including: a magnetic detection element for detecting rotor rotation position of a motor; a position signal amplifying circuit for amplifying an output signal of the magnetic detection element; an output circuit, a coil for a stator of the motor; a capacitor for storing charges; a rotation detection circuit for generating a pulse in synchronization with the rotor rotation position; a first flip flop circuit reset by an output pulse of the rotation detection circuit; a charging circuit for supplying charges to the capacitor; a first comparator circuit for inverting the first flip flop circuit to stop charging when a potential of the capacitor is turned by a charge current of the charging circuit to a predetermined first potential; a charging/discharging circuit for synthesizing a charging current and a discharging current by utilizing constant current difference and supplying the synthesized current to the capacitor mainly at a time of motor locking in which pulse generation in the rotation detection circuit has stopped; a second flip flop circuit for holding charged state and discharged state of the capacitor; a discharge transistor; an inversion detection transistor for detecting timing for transition from charged state to discharged state of the capacitor; a breaking/resetting circuit for breaking power distribution to the coil through the output circuit when the potential of the capacitor increases to a second potential that is larger than the first potential; a pulse circuit for generating a reset pulse when the potential of the capacitor decreases to a predetermined third potential that is lower than the first potential; a second comparator circuit with hysteresis for detecting that the potential of the capacitor has increased to the second potential and has decreased to the predetermined third potential; an inverter circuit; and an OR circuit for controlling the breaking/resetting circuit based on the OR of an output of the first flip flop circuit and an output of the second comparator circuit.
Burnout of the actuator coil can be definitely reduced by applying the conventional protection techniques described above to a motor driver IC.
However, with the technique of muting all coil outputs when a maximum output of the actuator coil is detected continuously for a certain period of time, overcurrent is not detected in a case where driving is continued immediately before the maximum output of the actuator coil, thus causing a risk of occurrence of burnout.
With the technique of monitoring a power current of a driver driving a plurality of actuator coils to thereby control a peak current, a risk of failure to detect overcurrent arises when there is bias in the driving current of each actuator coil.
With the technique of detecting a control signal of a driver with a DSP (Digital Signal Processor) in a software-based manner to thereby control a peak current, a driving current is indirectly detected, which results in an increase in variation in the driving current to a coil due to variation in a coil and a driver driving signal, thus causing a risk of failure to detect overcurrent with high accuracy.
With the technique of detecting a driving voltage to a coil to thereby control a peak current, variation in the driving current due to variation in the coil cannot be detected.
The conventional technology of Patent Document 1 is just technology of stopping operation of an output circuit upon detection that a motor unintentionally falls into stopped state when the motor rotation stops due to some external factor, and entails different essential configuration from that of the present invention.